The overall objective of this project is the study of the interaction of neural and local mechanisms in the cardiovascular control of systemic and regional pressure-flow relations. The studies proposed herein concern: a) determination of the relative effects of aortic arch and cardiopulmonary baroreceptors; b) interaction of carotid sinus and aortic arch baroreceptors; c) carotid sinus baroreflexes in chronic animals with special regard to the effects of anesthesia; d) interaction of local and neural mechanisms in the control of regional hemodynamics with emphasis on the effects of hypoxia. Studies (a,b) will be conducted in chloralose anesthetized dogs. Measurement of pulsatile pressure and flow will be made in the ascending aorta, celiac, mesenteric, renal and iliac arteries. Hemodynamic responses to variations in mean pressure in the isolated, perfused carotid sinuses will be obtained. The relative contribution of aortic arch and cardiopulmonary baroreceptors will be made by comparing responses before and after bilateral aortic nerve section and subsequent vagotomy. The interaction of carotid sinus and aortic arch baroreceptors on regional hemodynamics will be assessed with both regions isolated and perfused under control conditions. This interaction will be established by varying mean pressure in the two regions singly and in combination. The effects of pulse pressure in the two regions will be assessed. Responses to bilateral carotid occlusion will be obtained in unanesthetized instrumented animals to evaluate baroreflex sensitivity. The effects on occlusion responses of changes in mean arterial pressure produced by IV phenylephrine or nitroprusside will be determined. Alterations by pentobarbital, halothane and chloralose anesthesia will be studied. The interaction of local and neural mechanisms on hindlimb vascular resistance will be studied in pentobarbital anesthetized dogs. Studies will be conducted with: a) physiological or controlled constant flow perfusion (normal and low), b) controlled oxygen tensions (supranormal, normal, mild hypoxia and severe hypoxia) either local or systemic, and c) controlled carotid sinus pressures. Experimental data will be evaluated by factorial analysis and analysis of variance methods.